1. Field of the Invention
The present invention relates to new compounds containing alkoxysilane groups and urea groups and to their use as coatings, sealants, or adhesives.
2. Description of the Prior Art
Hydrolyzable organofunctional silanes are key components for linking conventional polymer chemistry with silicone chemistry. Compounds of technical importance for this purpose are in particular those corresponding to the formula EQU (RO).sub.3 Si--(CH.sub.2).sub.3 --Y
wherein
R is an alkyl group and PA1 Y is a functional group. PA1 Z represents COOR.sub.1 or an aromatic ring, PA1 R represents the residue obtained by removing the isocyanate groups from an organic monomeric polyisocyanate or a polyisocyanate adduct, PA1 R.sub.1 and R.sub.2 are identical or different and represent organic groups which are inert to isocyanate groups at a temperature of 100.degree. C. or less, PA1 R.sub.3 and R.sub.4 are identical or different and represent hydrogen or organic groups which are inert to isocyanate groups at a temperature of 100.degree. C. or less and PA1 n is an integer from 1 to 8. PA1 X represents identical or different organic groups which are inert to isocyanate groups below 100.degree. C., provided that at least one of these groups is an alkoxy group, preferably alkyl or alkoxy groups having 1 to 4 carbon atoms, more preferably alkoxy groups; PA1 Z represents COOR.sub.1 or an aromatic ring, preferably COOR.sub.1, PA1 R represents the residue obtained by removing the isocyanate groups from an organic monomeric polyisocyanate or a polyisocyanate adduct, PA1 R.sub.1 and R.sub.2 are identical or different and represent organic groups which are inert to isocyanate groups at a temperature of 100.degree. C. or less, preferably alkyl groups having 1 to 9 carbon atoms, more preferably methyl, ethyl or butyl groups PA1 R.sub.3 and R.sub.4 are identical or different and represent hydrogen or organic groups which are inert towards isocyanate groups at a temperature of 100.degree. C. or less, preferably hydrogen and PA1 n is an integer from 1 to 8, preferably 2 to 4 and more preferably 3.
Such compounds contain both hydrolyzable silyl groups, OR, which crosslink by "silane polycondensation" in the presence of moisture, and other functional groups, Y, which enable them to be chemically linked to conventional polymer materials. (See e.g., Angew. Chem. 98 (1986) 237-253.)
Hydrolyzable functional silanes corresponding to the above formula in which the functional group Y contains Zerewitinoff active H-atoms are potentially capable of modifying polyisocyanates. (See, e.g., WO 92/05212). Commercially available products suitable for this purpose contain NH.sub.2 and/or NH groups as Zerewitinoff active H-atoms. Also available are compounds containing SH groups.
Alkoxysilanes containing SH groups are described, for example, in GB-A-1,102,251; EP-A-0,018,094; DE-A-1,162,818; U.S. Pat. No. 3,590,065; U.S. Pat. No. 3,849,471; U.S. Pat. No. 4,082,790; U.S. Pat. No. 4,012,403; and U.S. Pat. No. 4,401,286. All alkoxysilanes containing SH groups have the unpleasant odor which is typical of mercaptans. The polymer may, therefore, have an unpleasant odor due to residues of these compounds.
.alpha.-Aminoalkyl silane derivatives which can be cross-linked by moisture may be prepared according to German Offenlegungsschriften Nos. 1,812,504 and 1,812,562. The functional silanes described there have, however, failed to achieve technical importance due to the complicated process for their synthesis.
Alkoxysilanes containing amino groups are described, e.g., in J. Org. Chem. 36 (1971), p. 3120; DE-A-1,152,695; DE-A-1,271,712; DE-A-2,161,716; DE-A-2,408,480; DE-A-2,521,399; DE-A-2,749,316; U.S. Pat. No. 2,832,754; U.S. Pat. No. 2,971,864; and U.S. Pat. No. 4,481,364. Common to all amino-functional silanes known in the art is the disadvantage of being extremely reactive with isocyanates. Therefore, it is difficult to react these alkoxysilanes with polyisocyanates due to the incompatibility, inhomogeneity and extremely high viscosities of the reaction products.
U.S. Pat. No. 5,554,709 discloses that amino-functional silanes can be reacted with certain NCO prepolymers, provided that the functionality of the prepolymer is less than 2.
U.S. Pat. No. 5,364,955 discloses that by initially reacting amino-functional silanes with maleic or fumaric acid esters to form secondary amino groups (i.e., aspartates), it is then possible to react these aspartates with NCO prepolymers without encountering incompatibility, inhomogeneity or extremely high viscosities in the reaction products. However, this reference does not disclose that it is possible to react all types of polyisocyanates with aspartates, i.e., polyisocyanate monomers and polyisocyanate adducts are not disclosed.
It is an object of the present invention to provide compounds containing urea and alkoxysilane groups that are either liquid or capable of being dissolved in commonly used organic solvents, are based on polyisocyanate monomers and/or polyisocyanate adducts, and do not suffer from the incompatibility, inhomogeneity and viscosity problems encountered with the prior art reaction products of isocyanates with alkoxysilanes containing NH groups. It is an additional object of the present invention to provide compounds containing alkoxysilane groups that can be cured by silane polycondensation to form coatings, sealants, and adhesives.
These objects may be achieved with the compounds containing alkoxysilane groups and urea groups according to the present invention described hereinafter. These compounds are prepared by reacting polyisocyanate monomers and/or adducts with aspartates (obtained by reacting aminoalkyl alkoxysilanes with maleic or fumaric acid esters) to form compounds containing urea groups.
It is surprising that the products according to the invention are liquid at room temperature because the corresponding products prepared by the direct reaction of polyisocyanate monomers and/or adducts with aminoalkyl alkoxysilanes are solids that cannot be dissolved with conventional coating solvents. The prior art, i.e., U.S. Pat. Nos. 5,554,709 and 5,364,955, only teaches that the reaction product of an NCO prepolymer with either an aminoalkyl alkoxysilane or an aspartate prepared from an aminoalkyl alkoxy silane is liquid. It does teach that it would be possible to convert the solid reaction products prepared from polyisocyanate monomer and/or adducts to liquid products by using the aspartate form of the aminoalkyl alkoxysilanes.